This is due a
relatively recent update in Chrome that encourages the use of secure protocols when sensitive information is being communicated. We've been upgrading all our websites to use SSL throughout, and the forum is currently going through the same process (albeit a bit slower since we are migrating the entire platform); until then you are most likely to see those warnings on the log-in page on certain devices.
This doesn't mean the connection is less secure than before, just that the secure protocol is a recommended upgrade which can prevent someone else on your network intercept communication with our servers.
Sorry for the technical answer, but please know we are fast at work on pushing the new platform and are excited to bring the upgrade as soon as possible